WEST SACRAMENTO (AP) – A northern California labor union says contracts talks with Raley’s supermarkets have broken down and a strike has been called.

Ellen Anreder, a spokeswoman for the United Food and Commercial Workers Union, said early Sunday that picket lines will begin at 6 a.m. PST.

The announcement came a few hours after both sides said the existing labor contract was being extended on an hour-by-hour basis at the request of the federal mediator.

But the union says in a statement released early Sunday that “by late on Saturday evening it had become obvious Raley’s offer to extend the contract for an additional three days and return to the bargaining table” was a delaying tactic.

On Saturday the two sides held a third day of bargaining aimed at heading off the first strike in Raley’s 77-year history.

WATCH: Raley’s Faces First Possible Strike In Company History

The grocer has 128 stores in Northern California and Nevada.

(Copyright 2012 The Associated Press.)